Document GB-1 183 316 discloses methods for the inductive soldering of heating wires placed in parallel with their collector conductors. In the first embodiment, the heating wires are fixed by bonding onto a glazing surface and the collector conductor—a thin strip of tinned copper—is positioned over the top. The soldering tool is guided over the same surface of the glazing with a constant stand-off distance along the collector conductor using spacer rollers. In the second embodiment, the heating wires and the collector conductors are inaccessible from the outside in a laminated glazing unit made up of two sheets of glazing and an adhesive layer. Here, electrical contact between the heating conductors and their collector conductors is to be made only after the laminated glazing unit has been produced. To achieve this, use is made of the ability of a magnetic field to transmit, without contact, through one of the sheets of glazing, the energy required to melt the solder; this sheet of glazing in this instance acts as the “spacer” for the hand-guided soldering tool.
It is known that such glazing is used especially in motor vehicle manufacture, but also in buildings. Other typical applications are, for example, the soldering of contact bases for connection lines. These are becoming increasingly small in order to save space in motor vehicle manufacturing and are often also provided with cable connections, which may prove awkward when soldering tools are being applied directly (see EP 477 069 B1). Likewise, electronic components such as amplifiers or the like are already soldered directly to antenna conducting fields printed onto an external surface of the glazing.
For technical reasons associated with manufacture and in order to be able to connect a plurality of connections towards the outside using a common multiple cable, several soldered assemblies or solder spots are usually positioned very close together (see DE 195 36 131 C2). Using conventional soldering tools, these assemblies or spots do, however, have to be soldered one after another individually.
However, applying soldering irons directly to the connection components concerned from the open “front face” is often a disadvantage, especially when—and above all in industrial-scale production with short pass times—incorrect positioning can occur as a result of the inevitable action of forces.
In the case of induction soldering, apparatus manufacturers do, however, typically recommend a high frequency of between 700 and 900 kHz depending on the thermal power to be applied. At the same time, the electrical power requirement is only relatively low (1 to 4 kW).
Tests carried out under the conditions of the possible applications discussed above with the recommended relatively high frequencies have not, however, made it possible to obtain satisfactory results. In particular, the conducting structures that act as soldered-connection faces on the surface of the lazing, which are made up of a thick baked-on layer of screen printing paste with a relatively high silver content, may heat up excessively and dissipate a great deal of heat while at the same time the components that are to be soldered have not yet become sufficiently hot. One cause could be that the conducting structure, or its material, has high absorption with respect to the waves generated by induction. The heating effect obtained by using high frequencies then either does not penetrate deep within a voluminous body or does so extremely slowly, but rather remains at the surface thereof (something also called the “skin effect”, see, in this respect, DE 694 30 275 T2, page 36). In consequence, the short pass times do not allow the required depth of penetration to the other face of the thick layer concerned to be achieved with any certainty.
Document DE 196 36 216 A1 describes a device and a method for the induction heating of components, particularly for hardening and soldering, in which an induction loop or coil is combined with a conducting body to deflect or orientate the magnetic field. The loop/coil is made up of a tubular material that is a good conductor of electricity, which is cooled during the soldering operation by a circulating cooling fluid. The operating or frequency range recommended for heating metals by induction is from 10 kHz to 10 MHz. In that document, however, just one application to the hardening of the edges of bored holes is described in detail. The conducting body mentioned forms a core that can be introduced into the respective bore. The document gives no other information as to the production of installations or methods for soldering using inductive heating.